Abstract

A probabilistic analysis of atmospheric transport and deposition patterns from two nuclear risk sites -- Kamchatka and Vladivostok -- situated in the Russian Far East to countries and geographical regions of interest (Japan, China, North and South Koreas, territories of the Russian Far East, State of Alaska, and Aleutian Chain Islands, US) was performed. The main questions addressed were the following: Which geographical territories are at the highest risk from hypothetical releases at these sites? What are the probabilities for radionuclide atmospheric transport and deposition on different neighboring countries in case of accidents at the sites? For analysis, several research tools developed within the Arctic Risk Project were applied: 1. isentropic trajectory model to calculate a multiyear dataset of 5-day forward trajectories that originated over the site locations at various altitudes; 2. DERMA long-range transport model to simulate 5-day atmospheric transport, dispersion, and deposition of ^137Cs for 1-day release (at the rate of 10^10 Bq/s); and 3. a set of statistical methods (including exploratory, cluster, and probability fields analyses) for evaluation of trajectory and dispersion modeling results. The possible impact (on annual, seasonal, and monthly basis) of selected risk sites on neighboring geographical regions is evaluated using a set of various indicators. For trajectory modeling, the indicators examined are: 1. atmospheric transport pathways, 2. airflow probability fields, 3. fast transport probability fields, 4. maximum possible impact zone, 5. maximum reaching distance, and 6. typical transport time fields. For dispersion modeling, the indicators examined are: 1. time integrated air concentration, 2. dry deposition, and 3. wet deposition. It was found for both sites that within the boundary layer the westerly flows are dominant throughout the year (more than 60% of the time), increasing with altitude of free troposphere up to 85% of the time. For the Kamchatka site, the US regions are at the highest risk with the average times of atmospheric transport ranging from 3 to 5.1 days and depositions of 10^-1 Bq/m2 and lower. For the Vladivostok site, the northern China and Japan regions are at the highest risk with the average times of atmospheric transport of 0.5 and 1.6 days, respectively, and depositions ranging from 10^0 to 10^+2 Bq/m^2. The areas of maximum potentially impacted zones are 30 x 10^4 km^2 and 25 x 10^4 km^2 for the Kamchatka and Vladivostok sites, respectively.